Bandwidth problem

Not sure if this is the right subforum so please put it in the right one if it isnt.

I just set up my Zotac AD02 + 320 GB + 4gb corsair DDR3 on my LG tv. Together with a Logitech DiNovo remote on Windows 7 64 bit.

I got XBMC working, Sickbeard, SabNZB , couchpotato not yet ( API errors ) . Now the problem is that if the mediapc is connected to the wifi ( cant run cables ) it slows the whole network down in such a matter that I cant even open a webpage on my other laptop or phone. My router(Ubee) doesnt have QoS options as far as I can see.

Even when SabNZB isnt running ( on pause ) it hogs it down a lot. Does XBMC use a lot of network resources? My files are on a 1TB 2.0 USB drive attached to it so it isnt pulling those files from the wife. Does it use a lot of internet resources to download pictures etc ( ALL THE TIME ) ?

Is there any sort of ( free) software where I can limit the bandwidth that each computer gets? And also in certain times? I have a 30 mbit connection. Lets say that the Media PC gets 18 mbit, the laptop 10 and my mobile devices 2. And at night that the Media PC gets 25 and the laptop 0 etc.